CN108370225A - Permanent-magnet self-starting motor and method of accessing for the permanent-magnet self-starting motor - Google Patents

Abstract

The invention relates to a permanent-magnet self-starting motor and a switch-on method for the permanent-magnet self-starting motor, preferably for motors having a power of at least 5 kW. In this case, the motor comprises a rotor and a stator with a stator winding, wherein the stator winding is designed as a pole-switchable rotating field winding. Generator-like braking torques that occur during asynchronous starting operations can be avoided by means of the pole-switchable rotating field winding. This is achieved by switching the pole-switchable rotating field winding during the start-up phase.

Description

Permanent magnet self-starting motor and connection method for the permanent magnet self-starting motor

technical field

The invention relates to a permanent-magnet-excited self-starting motor—hereinafter also referred to as a permanent-magnet-excited self-starting motor (PM-line-start motor)—and to a switching method for the permanent-magnet-excited self-starting motor.

Background technique

The permanent magnet self-starting motor - alternatively also sometimes called permanent magnet excitation self-starting motor, self-starting permanent magnet motor or LSPM-motor - is a three-phase electric-asynchronous motor with a short-circuited rotor, which The rotor contains additional permanent magnets in the rotor. After an asynchronous start, the permanent magnet self-starting motor is synchronized to the feed frequency and then operated in synchronous operation. The permanent-magnet self-starting motor fundamentally has minimal rotor and field losses, which results in a higher efficiency. Therefore, the permanent magnet self-starting motor combines the advantages of a robust asynchronous machine and a synchronous motor with less losses.

This type of motor has the ability of an asynchronous motor to generate an asynchronous starting torque and the ability of a synchronous motor to run at a speed that is synchronous to the rotating field.

Permanent magnet self-starting motors must be connected to the three-phase grid with a suitable switching method from a rated power of about 4 to 5 kW in order to reduce switching shocks in the grid and in the shafting.

A start-up method known from cage-rotor motors—for example a star-delta starter, a starting transformer or a soft starter—is a method that first reduces the motor voltage when starting up. These methods cannot be meaningfully used in permanent magnet self-starting motors. The reason for this lies in the physics of permanent magnet self-starting motors.

Permanent magnet self-starting motor is a combination of cage rotor motor and permanent magnet synchronous motor. After switching on, the permanent magnet self-starting motor is first started with the starter cage like a cage rotor motor. A final synchronization to the synchronous rotational speed follows the start-up process, and the permanent-magnet self-starting motor is then operated as a permanent-magnet synchronous motor with a correspondingly high efficiency.

During the asynchronous starting process, the permanent magnet rotor induces a sliding frequency voltage system into the stator winding, and the three-phase grid is actually short-circuited to this voltage system. As a result, in addition to the desired asynchronous torque of the starter cage, an additional generator-like braking torque results, which substantially hinders the starting process. The superposition of the two torque portions is schematically drawn in FIG. 1 .

The curve of the generator-like braking torque has a prominent brake saddle. This generator-type brake saddle is a real problem during the switch-on and start-up process with reduced voltage, and said generator-type brake saddle has only a very limited structural capacity in its order of magnitude. are affected and are also independent of the grid voltage.

Since the asynchronous torque decreases quadratically with the reduced voltage, but the height of the generator brake saddle remains constant, the start-up process may already be at the corresponding reduced voltage. The generator-style brake saddle ends up at the end. The asynchronous drive torque with the reduced voltage is not high enough to overcome the generator-like brake saddle. This can therefore lead to subsynchronous limiting cycles (oscillations around a rotational speed point in the subsynchronous rotational speed range) of the motor during the switch-on phase with the reduced voltage. In practice, this build-up on the generator-type brake saddle already takes place as soon as the voltage is reduced to 80 to 85%. Therefore, for permanent magnet self-starting motors, the method of only reducing the voltage cannot be used. The following task was therefore addressed: to develop an efficiently usable switching-on method for permanent-magnet self-starting motors which overcomes the aforementioned disadvantages.

So far, this task has not had to be solved, since permanent-magnet self-starting motors—quite contrary to their name “self-starting”—were primarily developed especially for variable-speed operation on U-f converters. Only in the last few years has the self-starting functionality been rediscovered in conjunction with the requirements for efficiency class motors (Effizienzklassemotoren). However, the permanent magnet starter motors currently on the market cover the lower power range up to about 5 kW. However, a switch-on method is not yet required for this power range, so that such motors do not suffer from the problems explained above.

Contents of the invention

The invention solves this problem by means of a permanent-magnet self-starting motor having the features of claim 1 .

Thus, the permanent magnet self-starting motor, which preferably has a power of at least 5 kW, comprises a rotor and a stator with stator windings, wherein the stator windings are implemented as a pole-switchable rotating field winding.

Generator-like brake saddles, which impede the starting of the motor, can thus be avoided in a switch-on method.

The pole-switchable rotating field winding preferably comprises a first winding stage and a second winding stage capable of being operated separately from each other, wherein the first winding stage possesses a The number of pole pairs, referred to as starting pole pair number p ₁ , differs from the number of pole pairs of the second winding stage, referred to below as operating pole pair number p ₂ .

Typically, the first winding stage is used for asynchronous starting of the motor and the second winding stage is used for synchronous operation of the motor. In this case, the advantage is that the first winding stage is designed in such a way that no generator-like brake saddle can be formed.

The braking action of the generator brake saddle in the starting phase is possible if the first winding stage used for starting the motor asynchronously has a starting pole pair number p ₁ which The number is inconsistent with the number of pole pairs p ₃ of the permanent magnet rotor. Therefore, during the starting phase, the stator winding and the starting cage operate as a purely asynchronous motor with the number of starting pole pairs p ₁ . The permanent magnet rotors are decoupled due to the different number of pole pairs. This decoupling prevents the formation of a generator-like brake saddle. Therefore, it does not occur that a braking torque counteracting the starting torque is generated during the starting process of the permanent magnet rotor.

After start-up, a switchover is made to the second winding stage, which preferably has the same number of pole pairs p ₃ of the permanent magnet rotor. Thus, in an advantageous embodiment of the invention, the number of active pole pairs p ₂ of the second winding stage is the same as the number of pole pairs p ₃ of the permanent magnet rotor. It is clear to a person skilled in the art that the second winding stage is provided for synchronous operation of the permanent magnet self-starting motor.

According to a further advantageous development of the invention, the number p ₁ of starting pole pairs of the first winding stage is smaller than the number p ₂ of working pole pairs of the second winding stage. Thus, for example, the ratio of pole pairs of the first to the second winding stage of the stator winding can be 1:2. However, this does not exclude a variant of the invention in which the number p ₁ of starting pole pairs of the first winding stage can also be greater than the number p ₂ of working pole pairs of the second winding stage.

According to a further development of the invention, the motor also includes a start control device, which is designed for a purposeful activation of the pole-switchable rotating field winding during the switch-on process of the motor. winding switching. A purposeful switching of the windings is preferably carried out here: from the first winding stage for starting the motor to the second winding stage for synchronous operation of the motor.

According to a further advantageous development of the invention, the start control device is also designed such that a phase or a time period is provided between switching from the first winding stage to the second winding stage, during which During phases or time periods, neither the first nor the second winding stage is supplied with energy, wherein the moment of switching to the second winding stage preferably takes place depending on the phase of the mains voltage.

The switching time has a decisive influence on the reconnection current surges which can occur with regard to the induced voltage (pole rotor voltage) when the phase of the grid voltage is taken into account.

In this case, the motor according to the invention can additionally comprise a first switch and a second switch for selectively closing or opening a line arranged between the individual winding stages and the mains voltage line, the first switch being connected to the first winding stage, and the second switch is connected to a second winding stage. Preferably, the first as well as the second switch can be actuated by the start control. The protector is particularly suitable as a switch.

According to an optional development of the invention, the respective ends of the first and second switches which are not connected to the associated winding are connected to each other and connected to the supply line via the mains switch. In this case, the mains switch is preferably also designed to be actuatable by a start control.

According to one specific embodiment, the motor can have an upstream circuit for reducing the voltage between the mains voltage line and the stator winding in order to limit the switching current or switching current, which switching current or switching current A current flow can occur, for example, when switching from the first winding to the second winding. In this case it is possible for the upstream circuit to be realized by a upstream connection impedance or a soft starter.

According to another optional feature, the stator winding is implemented as a Daland winding.

An embodiment of the stator winding in the form of a Dalland winding is advantageous because better utilization of the active components is achieved.

However, as an alternative to the one-piece construction of the stator winding in the form of a Dalland winding, the stator winding can also have two mutually separated windings which are each designed for a different number of poles.

According to an advantageous embodiment of the invention, the motor is designed such that the switching from the first winding to the second winding takes place supersynchronously (übersynchronously) depending on the synchronous nominal speed n ₁ of the permanent magnet self-starting motor . In this case, the nominal speed n ₁ is the ratio of the grid frequency f _netz divided by the number of pole pairs p ₂ of the second winding stage.

As a result, a reconnection current surge is kept as small as possible when switching from the first winding stage to the second winding stage.

To this end, the invention also relates to a method for switching on a permanent-magnet self-starting motor having the features of one of the aforementioned embodiments, wherein the method comprises the following steps:

(i) switching on the first winding stage to start the asynchronous start-up phase;

(ii) switching off the first winding stage to end said asynchronous start-up phase, and;

(iii) Switching on the second winding stage, which is designed for synchronous operation of the motor.

The aforementioned switch-on method furthermore preferably comprises the following steps between steps (ii) and (iii):

(iv) monitoring of the grid voltage and the induced pole-rotor voltage to determine switching times which permit a grid connection which is as shock-free as possible, wherein preferably

The switching time permits a grid connection that is as shock-free as possible when there is approximately a frequency identity between the pole rotor voltage and the grid voltage and the difference between the grid voltage and the frequency identity is small, that is to say at below a predetermined threshold.

Description of drawings

The invention and its developments are described in more detail below with reference to the drawings of preferred exemplary embodiments. show:

Figure 1: A quasi-static torque curve during asynchronous starting of a conventional permanent magnet self-starting motor;

Fig. 2: a kind of structural circuit diagram of permanent magnet self-starting motor according to the present invention through wiring;

Figure 3: Switching sequence of the switches depicted in Figure 2 at the start of the motor;

Figure 4: A torque (rotational speed) diagram of the starting process of a permanent magnet self-starting motor with winding switching according to the present invention;

Fig. 5: A kind of wiring modification scheme of permanent magnet self-starting motor according to the present invention;

Fig. 6: a kind of structural circuit diagram of the permanent magnet self-starting motor that has a kind of additional soft starter according to the present invention through wiring;

Figure 7: Wiring diagram of a wired permanent magnet self-starting motor whose pole-switchable stator winding is a Dalland winding;

Figure 8: A static torque (speed) diagram of the starting process of a permanent magnet self-starting motor with supersynchronous winding switching according to the present invention, and;

Fig. 9: A structural circuit diagram of a wired permanent magnet self-starting motor according to the present invention.

Detailed ways

FIG. 1 has already been explained in detail at the beginning of the description, and FIG. 1 shows the curve of the braking torque as a function of the rotational speed of the motor. The problem is that the asynchronous torque decreases quadratically with a decrease in voltage, but the braking torque induced by the permanent magnet rotor remains constant. Therefore, if one now wishes to provide a switch-on method—initially with a reduced voltage—there is the danger that the braking torque is greater than the asynchronous torque and counteracts the acceleration of the rotor.

FIG. 2 shows a schematic connection diagram of a permanent magnet self-starting motor with winding switching according to the present invention.

A total of three switches are identified, which are designed as breakers in the form of semiconductor breakers and/or mechanical breakers or as switching elements. Switches S1 and S2 feed the motor winding in such a way that two winding stages are produced for the permanent magnet self-starting motor. A third switch, designated grid, separates the entire line from the three-phase grid during the switching phase and when the drive is no longer in operation. The first winding stage connected to switch S1 is intended for asynchronous starting and is designed in such a way that practically no generator-like brake saddle can be formed. After the asynchronous start in the first winding stage, a switchover is made to the second winding stage, which is specially designed for synchronous operation of the motor. In this case, all switches—that is to say S1 , S2 and the “mains network”—are connected to a process control device that controls the actuation of the individual switches.

FIG. 3 shows the overall switch-on and start-up process, which is basically divided into four switching phases. As already briefly explained above, the process controller—for example in the form of a memory-programmable controller or a conventional relay controller—is responsible for the desired switching sequence of the switches. If the first winding stage of the stator winding has a different number of pole pairs than the permanent magnet rotor, suppression of the generator-type brake saddle, which is typically in switching phase 1, is possible form. In phase 2, the stator winding is taken off the grid. In this case, the mains switches or switch S1 can be placed in their respective open positions simultaneously or sequentially. In phase 3, the stator winding is switched with S2 into the second winding stage, but the mains switch remains in its open position. The second winding stage now has the number of pole pairs of the permanent magnet rotor in order to implement a synchronous operation of the permanent magnet self-starting motor. In order to generate an inrush current surge that can be as small as possible, it is expedient to carry out a comparison of the mains voltage and the induced voltage in phase 3 . Even though the two voltages may have different frequencies, the transition to phase 4 (closing of the grid breaker in phase 4) should only take place if the phases of the two voltages are as favorable as possible to each other - that is to say all The two three-phase voltage systems described above have as much as possible the same phases.

In phase 4, therefore, the second winding is connected to the mains voltage via S2, which thus takes over, so to speak, the rotor started by the first winding.

Figure 4 shows this start-up process quasi-statically in a torque (rotational speed) diagram (M(n)-Diagramm) to illustrate the case where the number of pole pairs of the two winding stages of the stator winding has a ratio of 2:1 . In this case, it therefore applies that the number p ₁ of starting pole pairs of the first winding is twice as large as the number p ₂ of working pole pairs of the second winding. In this case, basically two curves are identified, which show the rotational speed of the motor on the abscissa and the torque produced by the motor on the ordinate. The curve designated S1 corresponds to the characteristic curve of the first winding stage, and the curve designated S2 corresponds to the characteristic curve of the second winding stage. The curve shown in dotted line and marked with W is the load characteristic curve here.

In a switch-on method according to the invention for a motor with winding switching, the characteristic curve S1 is followed from rotational speed 0 until the switching process, which is indicated by a double dashed line and a transparent upward-pointing triangle Transform to the characteristic curve of the second winding.

As a result, the generator brake saddle of the characteristic curve S2 of the second winding stage (which is designed for synchronous operation of the motor) is skipped and only used in a certain range of the characteristic curve , the area no longer has brake saddles.

The described switch-on method with winding switching now additionally makes it possible to reduce the voltage during the switch-on and start-up phase without the risk that the generator-like brake saddle stops the start-up process, in particular with reduced The starting process of the voltage.

FIG. 5 shows a further illustration of an embodiment according to the invention which, instead of a mains switch, has a forward circuit controllable by the process control device. The pre-circuit is not only connected to the switch S1, but also connected to the switch S2. Just like the circuit shown in FIG. 2 , the goal is to disable the generator-like brake saddles that occur during the start-up phase during the switch-on method. For this purpose, switchable stator windings are used during start-up. The first winding stage is switched via the switch S1 and is designed in particular for an asynchronous starting process and is designed such that a generator-like brake saddle cannot be formed. To limit the inrush current, a voltage-reducing upstream circuit can be arranged between the mains network and the stator winding, wherein in the simplest case this is a upstream connection impedance or a soft starter.

As already explained above, after the asynchronous start-up, the first winding stage is switched off via the switch S1 and the second and last winding stage is switched on using the switch S2. This is specifically designed for synchronous operation. Likewise, in order to limit the reconnection current during the changeover to the second winding stage, a voltage-limiting upstream circuit can be used between the network and the stator winding.

Suppressing a generator-like brake saddle during the starting phase is possible if the stator winding has a starting pole-pair number p ₁ in the first winding stage which corresponds to the pole-pair number of the permanent magnet rotor The number p ₃ is inconsistent. During the starting phase, the stator winding with the number of starting pole pairs p1 and the starting cage are thus operated as a purely asynchronous motor. The permanent magnet rotors are decoupled due to the different number of pole pairs. After start-up, a switch is made to the second winding stage, in which the stator winding now has the number of active pole pairs p2 of the permanent magnet rotor p3. Thus, the stator winding of the second winding stage, which is provided for synchronous operation of the permanent-magnet self-starting motor, has a number of pole pairs p2. In order to avoid a generator-like brake saddle, the stator winding of the permanent-magnet self-starting motor is designed as a pole-switchable rotating field winding.

An embodiment is basically conceivable here, which has two separate stator windings, each of which is designed for a different number of pole pairs.

FIG. 6 shows a variant of the invention with a soft starter that reduces the motor voltage and the switch-on current and increases it after a voltage-time ramp up to the direct mains voltage. Jumper such a soft starter after startup.

FIG. 7 shows the wiring arrangement of a permanent magnet self-starting motor according to the invention, in which the stator winding is designed as a Dahlanderwick winding. This has the advantage that a better utilization of the active components results.

According to FIG. 7 , the stator winding consists of two partial windings whose realized winding ends U _1,2,3 , V _1,2,3 and W _1,2,3 can be Connection to each symmetrical three-phase electrical circuit (star-or delta circuit, double star-or double-delta circuit). FIG. 7 also shows a voltage-limiting upstream circuit between the mains network and the stator winding for additionally limiting the switching-on or switching-on current. However this is optional.

In order to keep a reconnection current surge as low as possible when switching from the first winding stage to the second winding stage, the switching is related to the synchronous rated speed n ₁ =f _netz /p of the permanent magnet self-starting motor ₂ is implemented hypersynchronously. A variant of the switching method is therefore only possible if the number p ₁ of starting pole pairs of the first winding stage is smaller than the number p ₂ of operating pole pairs of the second winding stage. This variant of the switch-on method can therefore be used for permanent-magnet self-starting motors with a number of pole pairs p ₂ ≧2.

Figure 8 shows a starting process in the static torque (speed) diagram (M(n)-Diagramm), where characteristic curve S1 shows the characteristic curve of the first winding stage and characteristic curve S2 shows the second The characteristic curves of the two-winding stage, and the characteristic curves embodied in dashed lines, show the load characteristic curves.

According to FIG. 8 , the stator winding is first connected to the three-phase grid in the first winding stage directly or via an optional upstream circuit. The stator winding is designed with respect to the first winding stage in such a way that a standstill operating point results with a load characteristic above the synchronous nominal speed n ₁ =f _netz /p ₂ . In a next step, the stator winding is disconnected from the grid and first switched into the second winding stage by means of the process controller. The stator winding now has the number of pole pairs of the permanent-magnet rotor and the permanent-magnet rotor induces a pole-rotor voltage with a frequency p ₂ ·n that is dependent on the current rotational speed into the stator winding.

Since the motor is not yet connected to the grid, the drive is suppressed due to the load characteristic. This is recognized at the slippage of the operating point which lies at the intersection of characteristic curve S1 and load characteristic curve W _last and which moves in the direction of a lower rotational speed on load characteristic curve W _last .

The task of the process controller is then typically to monitor the grid voltage and the induced pole rotor voltage in the sense of a grid connection that is as shock-free as possible. If there is approximately equal frequency and the difference between the grid voltage and the pole rotor voltage is as small as possible, then the stator winding of the permanent magnet self-starting motor in the second winding stage is connected to the three phases directly or via a preceding circuit on the grid. The operating point therefore spans from the characteristic curve S1 of the first winding to the region of the characteristic curve S2 of the second winding without having to pass through the generator-type brake saddle of the characteristic curve S2 .

Starting from the rotary pump drive in FIG. 8 and assuming a stator winding according to the Dalland principle, the first winding stage can be designed as a delta circuit and the second winding stage as a double star circuit.

FIG. 9 shows a protection circuit for the main circuit for this purpose. Apart from a possible pre-circuit for additional reduction of the switch-on current and the switch-on current (which is optionally shown in FIG. 8 ), only three a main protector.

The process control unit is responsible for the necessary switching sequence of the switch-on methods, which process control unit can be implemented, for example, by an SPS (programmable memory control unit).

In a first step, the stator winding is switched on in the first winding stage. If a pre-circuit for limiting the inrush current is required, this pre-circuit is then switched off.

In a subsequent second step, the asynchronous start-up phase is switched off. This is typically achieved by interrupting the power input to the first winding stage.

In a third step, the stator winding is switched from the first winding stage to the second winding stage. The switches or protectors S1 and S2 are correspondingly switched for this purpose. For the second winding stage, the electrical star point is generated via switch or protector S3.

The grid voltage and the induced pole rotor voltage are then monitored in order to enable a reactivation that is as shock-free as possible.

Then, the switch-on takes place at an advantageous point in time. In this case, the second winding stage is therefore connected to the mains voltage. If a pre-circuit is required for suppressing the reactivation current or making the current, this pre-circuit is disconnected in a subsequent step.

Claims (15)

1. permanent-magnet self-starting motor, it is therefore preferred to have at least power of 5kW, including：

One rotor and a stator with stator winding,

It is characterized in that, the stator winding is implemented as the changeable rotating field winding of magnetic pole.

2. motor according to claim 1, wherein the changeable rotating field winding of the magnetic pole include the first winding grade and Second winding grade, the first winding grade and the second winding grade can be run disconnected from each otherly, and the first winding grade is gathered around Have and starts number of pole-pairs p₁, the work number of pole-pairs p of the starting number of pole-pairs and the second winding grade₂It differs.

3. motor according to claim 2, wherein the first winding grade is used for the asynchronous startup of motor, and second Operation of the winding grade for the synchronization of motor.

4. motor according to claim 2 or 3, wherein the starting number of pole-pairs p of the first winding grade₁With the number of poles of p-m rotor p₃It is inconsistent, and the work number of pole-pairs p of the second winding grade₂Preferably with the number of poles p of p-m rotor₃It is identical.

5. motor according to any one of claim 2 to 4, wherein the starting number of pole-pairs p of the first winding grade₁Less than second The work number of pole-pairs p of winding grade₂。

6. motor according to any one of the preceding claims, which includes a kind of process control equipment in addition, described Process control equipment is designed thus：The changeable rotating field winding of magnetic pole is carried out during the connection process of motor has mesh Winding switching, wherein preferably implementing purposive winding switching below：From the first winding of the startup for motor Grade is switched to the second winding grade of the synchronous operation for motor.

7. motor according to claim 6, wherein the process control equipment is designed thus in addition：From first around A kind of stage is arranged between the switching of the second winding grade in group grade, is neither first nor be the second winding grade in this stage Supplying energy carries out while the phase of network voltage is preferably depended at the time of wherein being switched in the second winding grade.

8. motor according to any one of the preceding claims, which includes first switch and the second switch, institute in addition It states first switch with the first winding grade to be connected, the second switch is connected with the second winding grade, wherein first and second open Pass can preferably be manipulated by a kind of process control equipment.

9. motor according to claim 8, wherein the described first and second ends switching, far from winding mutually interconnect It connects, and is connected in supply line by a power network switch, wherein the power network switch can preferably pass through the process Control device is manipulated.

10. motor according to any one of the preceding claims, wherein a kind of front end circuit is arranged, for reducing in power grid Voltage between voltage circuit and stator winding, to limit turn-on current or again turn-on current, the front end circuit is herein Preferably realized by preposition connection impedance or a kind of soft strater.

11. motor according to any one of the preceding claims, wherein the stator winding is in the form of Da Lande windings Implement.

12. the motor according to any one of preceding claims 1 to 10, wherein there are two mutually for stator winding tool The winding of separation, they are separately designed for different numbers of poles.

13. the motor according to any one of preceding claims 2 to 12, wherein the motor or the process control Device is designed thus：The rated speed n of synchronization about permanent-magnet self-starting motor₁Implement to switch supersynchronously, and institute State rated speed n₁It is：n₁=f_netz/p₂, wherein

f_netzIt is mains frequency, and

p₂It is the work number of pole-pairs of the second winding grade.

14. the method for accessing of permanent-magnet self-starting motor, the permanent-magnet self-starting motor has any one of preceding claims institute The feature stated, wherein the described method comprises the following steps：

（i）The first winding grade is connected, to start asynchronous startup stage；

（ii）The first winding grade is cut off, to terminate the asynchronous startup stage, and；

（iii）The second winding grade is connected, operation of the second winding grade designed for the synchronization of motor.

15. method of accessing according to claim 14, wherein the method is in step（ii）With（iii）Between additionally wrap Include following steps：

（iv）Monitoring network voltage and the pole wheel voltage incuded, to determine switching instant, which permits a kind of A kind of power grid access as shock-free as possible is preferably permitted in shock-free power grid access as far as possible, wherein switching instant, when It is equivalent in the presence of about frequency between pole wheel voltage and network voltage, and the difference between network voltage and frequency are equivalent is very It is small, that is under predetermined threshold value when.